Rechargeable batteries manufactured from laminates of solid polymer electrolytes and sheet-like anodes and cathodes display many advantages over conventional liquid electrolyte batteries. These advantages include lower overall battery weight, high power density, high specific energy, longer service life, as well as being environmentally friendly since the danger of spilling toxic liquid into the environment is eliminated.
Solid polymer electrochemical cell components include positive electrodes, negative electrodes and a separator material capable of permitting ionic conductivity such as a solid polymer electrolyte sandwiched between each anode and cathode. The anodes (or negative electrodes) and cathodes (or positive electrodes) are made of material capable of reversibly intercalating alkali metal ions.
Such an advanced battery system typically consists of a series of extremely thin film laminates of anode material, polymer electrolyte separator, cathode material and current collector assembled together as a multi-layer construction in either a flat roll configuration, a jelly roll configuration or a flat stack configuration to form a battery. Individual electrochemical laminates are typically mono-face or bi-face. A mono-face electrochemical laminate consists of a current collector, a cathode, a polymer electrolyte separator, and an anode covered with an insulating polypropylene film to insulate the electrochemical laminate from the adjacent one for preventing short circuits. A bi-face electrochemical laminate consists of a central current collector having a cathode layer on both sides, a polymer electrolyte separator adjacent each cathode layer, and an anode layer adjacent each electrolyte separator. In a bi-face laminate, the insulating polypropylene film is eliminated since the risk of short-circuits between the anode and the cathode of adjacent laminates is removed. A bi-face laminate assembly typically provides a higher energy density.
For large batteries (500 gr or more), the preferred configuration is a flat stacked multi-layer assembly of bi-face laminate for its high energy density and for its ability to be shaped into a limited volume.
Numerous methods of assembling laminates into cells and batteries have been devised and/or investigated. U.S. Pat. No. 5,100,746 discloses a method of assembling the anode, cathode, current collector and electrolyte separator layers are co-laminated using a series of pressure rollers, the assembly thereafter being coiled to form a battery; however, the assembly could be cut and stacked.
U.S. Pat. No. 6,030,421 discloses a previously laminated mother-battery containing an anode of metallic lithium or sodium, a composite cathode, a polymer electrolyte that acts as a separator between the electrodes, and a current collector. The laminated mother-battery is thereafter subjected to a sharp mechanical cutting out to give thin polymer electrolyte batteries.
These documents disclose how to assemble the laminates themselves but do not teach precisely how to properly superpose or flat-stack the laminates to form batteries.
U.S. Pat. No. 6,547,229 discloses a stacking apparatus and method employing one or more stations, each including a stationary stacking platform or a conveyor upon which spaced-apart pucks are coupled for travel thereon. A product delivery apparatus drives one or more movable webs to which segmented product sheets are removably affixed. The product delivery apparatus includes one or more rotatable lamination interfaces associated with each of the stations for transferring product sheets from the webs to the pucks on a repetitive basis to produce a stack of product sheets on the respective pucks. Each of the segmented product sheets may define. all or a portion of an electrochemical cell, the latter including layers of film or sheet material, wherein a portion of each of the layers is provided with a bonding feature. A puck need not be in motion during the transfer of the product sheet from the lamination roll to the puck. The puck may or may not be attached to a conveyor, but the conveyor need not be in motion during the lamination or stack building process. In this case, a roller is moved across the puck and simultaneously rotated so a point on the surface of the roller interfaces with the puck at the same location on each pass.
WO 02/43179 discloses an apparatus and method for rotatably cutting and/or laminating layered structures or sheet material supported by webs. A rotary converting apparatus and method converts a web comprising a cathode layered structure and a web comprising an anode layered structure into a series of layered electrochemical cell structures supported by a release liner. Employment of a rotary converting process provides for the creation of a product having a finished size, without need for downstream or subsequent cutting.
These two documents disclose methods of stacking components of laminates using a rotary device. This type of rotating mechanism is however often unreliable to produce precise assembly.
There are numerous difficulties to overcome when stacking extremely thin sheets together to produce electrochemical cells. First, each layer must be precisely aligned with the other layers in order to have a properly assembled stack that can be electrically connected with ease and within which no electrical short circuit will occur due to misalignment of the plurality of layers. A rotary system is inherently unable to provide the precise stacking of each layer required for electrochemical cell assembly. Secondly, when stacking the various layers of the electrochemical cell together, it is imperative that air not be trapped between two layers. Air entrapment will prevent proper contact between the various layers thereby reducing the capacity of the electrochemical cell as well as creating uneven surfaces that may cause further problems in subsequent assembly steps. Thirdly, the components, i.e. thin films of cathode, anode and electrolyte separator, are sticky and are difficult to handle without ripping or corrupting.
Thus there is a need in the polymer battery industry for an efficient method and apparatus for stacking polymer electrochemical laminates and constituents thereof to form polymer electrochemical cells and batteries.